Igniting electrode arrangement and method



Jan. 20, 1942. l.. K. MARSHALL IGNITING ELECTRODE ARRNGEMEN'II AND METHOD Filed Feb.4 2l, 1939 `LAuR Nc: .MARSHALL Bv wyw ATTY.

Patented Jan. 20, 19,42

ELECTRODE ARRANGEME AND METHOD IGNITING Laurence K. Marshall, Cambridge, Mass., as signor to Raytheon Manufacturing Company, Newton, Mass., a corporation of Delaware Application February 21, 1939, Serial No. 257,645 claims. (C1. 25u-27.5)

.This invention relates to a novel igniting electrodearrangement for starting an arc spot on apool type cathode. The igniting electrode is of the type which is separated by an insulating Wallfrom the cathode, and initiates an arc b-y means of ahigh voltage impressed between the cathode and the i-gniting electrode. In devices of this kind, difficulties have been encountered in securing long life. After ycomparatively short periods ,ofloperati-on, voltages which initially would produce fairly reliable starting were'no longer suicient, and the starting became erratic.

"This effect became progressivelyworse until the tion will be best understood from the following c `description of an exemplication thereof, reference being had to the accompanying drawing,

whereinthe figure is` a cross-section. of a tube embodying the` invention, together `with a dia- E grammatic representation of a circuit with which said tube may be used. i

The tube illustrated ,comprisesa sealed envelope I, a pool type cathode 2, preferably. con. sisting of a` pool of mercury, and an anode .3.

In order to provide means for initiating an arc spot on the surface'of the cathode pool 2, the tube is provided with an igniting electrode 4, consisting of a rod of conducting material sealed through the bottom Wall of the envelope I. 'Ihe igniting electrode 4 is separated' and insulated from the cathode pool 2 by means of an insulating layer 5 covering the surface of the igniting electrode 4. Thisinsulating coating or layer is preferably made of glass sealed tothe surface of said igniting electrode. together with its insulating coating, are preferably constructed in accordance with the copending application of Percy L. Spencer, Serial No. 251,069, led January 16, 1939, in which the insulating layer 5 is described as having a thickness of the order of ten mils or less. However, it is to be understood that the present invention is not limited to this particular construction of be made to it.

" up and maintain said cathode spot if the voltage could likewise be utilized. External electrical connection may bemade to the cathode 2 through a pair of lead-in conductors 6--6 sealed through the lower wall of the envelope I and projecting into the pool 2. External electrical connection mayk also bev made to the anode 3 through the anode lead-in 1 sealed through the upper end of the envelope I. Inasmuch as the igniting electrode 4 is likewisesealed through the lower wall of the envelope I, direct electrical connection may In tubes of the type describedrabove, the application of a comparatively high voltage to the igniting electrode 4 will initiate a cathode spot on the mercury pool 2, and the anode 3 will pick impressed onl the anode-3 is-positive. The initiation of the cathode spot occurs at the surface of the mercury pool 42 substantially where the insulating member 5 emerges from said surface. In prior arrangements it has been` found that after a comparatively short period of operation, the starting of the arc spot became erratic and the tubes had a short operating life. I have found., however, that this difficulty can be substantially eliminated by producing relative motion between the surface of the insulating member 5 and the surface of the mercury pool 2 at the point where the arc spot tends to form. As pointed out above, this consists of a region surrounding the circumference of the insulating member 5 as it'emerges from the surface of the mercury pool 2. Ihave found that by producing such a motion, not only is the life` of the `tube lengthened but also the tube `is'made more sensitive in that lower voltages applied to the igniting electrode 4 will pro- I duce reliable ignition of the arc spot.

The igniting electrode,

In accordance with my present understanding of the theory of operation of` these tubes, the novel results described above are due substantially to the following reasons. I believe that the erratic behavior of the tubes andthe termination of the life thereof are due to thecontamination of the surface of the insulating member 5 at the region where the arc` spot tends to form. This` contamination appears to be due, at least in part, to the accumulation of impurities on the surface of the mercury pool 2. If these impurities are permitted to come into intimate contact with the insulating member 5, under the action of the arc these impurities attach themselves to the surface of the insulating member, and thus desensitize it. I believe that by producing the relative motion described above, these impurities are igniter inasmuch as larger thicknesses of glass washed away from the surface of the insulating member 5, and are thus kept from coming into intimate contact with said insulating member. It may be possible that if small amounts of impurities are driven out from the insulating mem- 'ber 5 itself, such; impurities likewise will be washed away from the insulating mem-ber which is thus maintained in a clean and sensitive condition. The mere mechanical motion of the mercury relative to the insulating member likewise appears to increase the sensitivity of the device, enabling lower igniting voltages to be used.

The arrangement shown in the drawing illustrates one mode of producing the necessary relative motion. Around the insulating member 5 is disposed an elongated tubular member 8 which `may be formed of any suitable material, such as, for example, a metal. This tube is open at its upper and lower ends so that mercury may freely.

circulate therethrough. 'Ihe tube 8 may be conveniently supported by being welded at its lower end to the two cathode lead-in conductors 6 6. Surrounding the tube 8 is a plunger 9 made of magnetic material. The plunger 9 is provided with a central bore which fits fairly closely around the tube 8 but which permits the member 9 to slide freely along said tube. The outer circumference of the member 9 likewise is designed to t closely within the lower extensiony I formed on the sealed envelope I. A slight clearance is left between the inner walls of the eX- tension II] and the outer diameter of the plunger 9 in order that the plunger 9 may slide freely within said extension III. The clearances between the plunger 9, the extension IIJ, and the tube 8 are made sufficiently small, however, so that mercuryA cannot flow freely through the intervening spaces. The plunger 9 is provided with `one or more bores II extending through the plunger 9, each of said bores terminating in an upper opening I2 of somewhat smaller diameter than the corresponding bore II. In each of the Abores II is placed a ball I3 which may be made of some suitable material, such as, for example, steel. In order to prevent the balls I3 from being pushed out of the bores II, a strip I 4 may be welded across the lower end of each bore I I. Of course it is to be understood that the width of each strip I4 is considerably less than the lower opening in the bore II, so that a free flow of mercury through said opening is permitted. In order to bias the plunger 9 to its proper position, a coil spring I5 is interposed between the lower face of said plunger 9 and the lower wall of the envelope I. If the plunger 9 is made of a material which has a tendency to float, the coil spring I5 should be anchored to the lower wall ofV the envelope I and also to the lower surface of the plunger 9. In order to actuate the plunger 9, the extension I0 of the envelope I is surrounded by an actuating coil I6 fed from a source of pulsating current I'I. The coil I6 is disposed somewhat below the deenergized position of the plunger 9.

When the coil I6 is supplied with a pulse of current from the source I1, the plunger 9 1s pulled down by the magnetic field created in the coil I6. The balls I3 close the opening I2, and thus mercury is trapped between the lower surface of the plunger 9 and the lower wall of the envelope I. The mercury so trapped is therefore pushed up through the tube 8, as indicated by the arrows therein, and ejected through the opening in the top of the tube 8. Upon the cessation of said current'l pulse, the coil I6 is deenergized and the plunger 9 moves upwardly, due to the pressure exerted by the spring I5 which previously had been compressed upon the downward motion of said plunger. Upon said upward motion, the balls I3 are pushed away from the openings I2 and the mercury above the plunger 9 can flow freely through said openings to the lower portion of the extension I0. Subsequent pulses of current supplied to the coil I6 produce additional pulses of mercury flow up through the tube 8. The pumping action described produces a flow of mercury around the insulating member 5 at the point where said insulating member emerges from the surface of the pool 2. This relative motion produces the various novel results which I have described above.

The tube illustrated may be utilized in a large number of circuits, one of which is shown diagrammatically. This circuit consists of a power transformer I8 having a primary winding I9 connected to a suitable source of alternating current, and a secondary winding 20. One end of the secondary winding is connected to the leadin 1 and thus to the anode 3, while the other end of said secondary winding is connected through a load 2I to the two cathode leads 6-6 which' are connected together. An igniting voltage may be impressed between the igniting electrode 4 and the cathode pool 2 from an igniting voltage control 22 which is energized through conductors 23-23, preferably from the same alternating current source as that which supplies the primary winding I9. By supplying igniting impulses of proper phase to the igniting electrode 4, an arc is initiated during each positive voltage swing of the main anode 3, and thus a controlled discharge current passes between the cathode 2 and the anode 3, which current is in turn delivered to the'load 2I.

Of course it is to be understood that this invention is not limited to the particular arrangement as described above inasmuch as many equivalents will suggest themselves to those skilled in the art. Various other forms of igniting electrode structure, which are immersed in the cathode pool and project through its surface, could be used and various other modes of producing relative motion between the mercury and the igniting electrode structure could likewise be devised. It is accordingly desired that the appended claims be given a broad interpretation commensurate with the scope of the invention within the art.

What is claimed is:

1. The method of operating an arc discharge device of the type having a liquid pool cathode, and igniting means of the electrostatic type comprising an electrode adjacent the surface of said cathode and separated therefrom by an insulating wall, which comprises producing relative motion between the cathode liquid and said insulating wall at the surface of said cathode in a direction substantially parallel with the sur` face of said insulating wall during the passage of the discharge from said cathode.

2. The method of operating an arc discharge device of the type having a liquid pool cathode, and igniting means of the electrostatic type comprising an electrode adjacent the surface of said cathode and separated therefrom by an insulating wall, which comprises producing relative motion between the cathode liquid and said insulating wall at the surface of said cathode in a direction substantially parallel with the surface of said insulating wall throughout the operation of said device.

3. The method of operating an arc discharge device of the type having a liquid pool cathode, and igniting means of the electrostatic type comprising an electrode adjacent the surface of said cathode and separated therefrom by an insulating wall which comprises moving the cathode liquid relative to 'said insulating wall at the surface of said cathode in a direction substantially parallel with the surface of said insulating wall durirg the passage of the discharge from said catho e. j

4. A11 arc discharge` device comprising an anode, a liquid pool cathode, and igniting means of the electrostatic type comprising an electrode adjacent the surface of said cathode and separated therefrom by an insulating wall, and means for producing relative motion between the cathode liquid and said insulating wall at the surface of said cathode in a direction substantially parallel with the surface of said insulating wall during the passage of the discharge from said cathode. l

5. An arc discharge device comprising an anode, a liquid pool cathode, and igniting means of the electrostatic type comprising an electrode adjacent the surface of said cathode and separated therefrom by an insulating wall, and liquid pumping means for moving the cathode liquid relative to said insulating wall at the surface of said cathode.

6. An arc discharge device comprising an anode, a liquid pool cathode, and igniting means of the electrostatic type comprising an electrode adjacent the surface of said cathode and separated therefrom by an insulating wall, and pumping means for moving the cathode liquid relative to said insulating wall at the surface of said cathode.

7. The method of operating an arc discharge device of the type having a liquid pool cathode, and igniting means of the electrostatic type comprising an electrode structure immersed in said pool and projecting through its surface, which comprises producing relative motion between the cathode liquid and said igniting electrode structure at the surface of said cathode in a direction substantially parallel with the surface of said igniting electrode during the passage of the discharge from said cathode.

8. The method of operating an arc discharge device of the type having a liquid pool cathode, and igniting means of the electrostatic type comprising an electrode structure immersed in said pool and projecting through its surface, which comprises moving the cathode liquid relative to said igniting electrode structure at the surface of said cathode in a direction substantially parallel with the surface of said igniting electrode during the passage of the discharge from said cathode.

9. An arc discharge device comprising an anode, a liquid pool cathode, and igniting means of the electrostatictype comprising an electrode structure immersed in said pool and projecting through its surface,and means for producing relative motion between the cathode liquid and said igniting electrode structure at the surface of said cathode in a direction substantially parallel with the surface of said igniting electrode during the passage of the discharge from said cathode.

10. The method of operating an arc discharge device of the type having a liquid pool cathode, and igniting means of the electrostatic type comprising an electrode adjacent the surface of said cathode and separated therefrom by an insulating wall, which comprises producing relative motion between the cathode liquid and said insulating wall at the surface of said cathode in a direction substantially parallel with the surface of said insulating wall.

11. The method of operating `an arc discharge device of the type having a liquid pool cathode, and igniting means of the electrostatic type comprising an electrode adjacent the surface of said cathode and separated therefrom by an insulating wall which comprises moving the cathode liquid relative to said insulating wall at the surface of said cathode in a direction substantially parallel with the surface of said insulating wall.

1,2. An are discharge device comprising an anode, a liquid pool cathode, and igniting means of the electrostatic type comprising an electrode adjacent the surface of said cathode and separated therefrom by an insulating wall, and means for producing relative motion between the cathode liquid and said insulating wall at the surface of said cathode in a direction substantially parallel with the surface of said insulating Wall.

13. The method of operating an arc discharge device of the type having a liquid pool cathode, and an igniting electrode structure immersed in said pool and projecting through its surface, which comprises producing relative motion between the cathode liquid and said igniting electrode structure at the surface of said cathode in a direction substantially parallel with the surface of said igniting electrode structure.

14. The method of operating an arc `discharge device of the type having a liquid pool cathode,

and an igniting electrode structure immersed in said pool andprojecting through its surface, which comprises moving the cathode liquid relative to said igniting electrode structure at the surface of said cathode in a direction substantially parallel with the surface of said igniting electrode.

15. An arc discharge device comprising ananode, a liquid pool cathode, and an igniting electrode structure immersed in said pool and projecting through its surface, and means for producing relative motion between the cathode liquid and said igniting electrode structure at the surface of said cathode in a direction substantially parallel with the surface of said igniting electrode structure.

LAURENCE K. MARSHALL. 

